feat: Implement a strategy to select the language/culture for each request in a localized ASP.NET Core app

.env.example

@@ -6,7 +6,6 @@ FRONTEND_APP_BASE_URL=http://localhost:80/
 MAX_DAYS_IN_CALENDAR=60
 BUSINESS_NAME=World Dental CO
 DENTAL_SERVICES_IMAGES_PATH=/app/dental_services
-LANGUAGE=es
 PLUGINS="
 Plugin.ChatBot.dll
 Plugin.AppointmentReminders.dll

DentallApp.sln

@@ -42,6 +42,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Elements", "Soluti
 		.env.example = .env.example
 		tests\IntegrationTests\.env.test = tests\IntegrationTests\.env.test
 		tests\IntegrationTests\.env.test.example = tests\IntegrationTests\.env.test.example
+		src\HostApplication\appsettings.json = src\HostApplication\appsettings.json
 		Directory.Build.props = Directory.Build.props
 		Directory.Packages.props = Directory.Packages.props
 	EndProjectSection

src/HostApplication/Extensions/AuthenticationJwtBearer.cs

@@ -2,7 +2,9 @@
 
 public static class AuthenticationJwtBearer
 {
-    public static IServiceCollection AddAuthenticationJwtBearer(this IServiceCollection services, AppSettings settings)
+    public static IServiceCollection AddAuthenticationJwtBearer(
+        this IServiceCollection services, 
+        AppSettings settings)
     {
         services.AddAuthentication(options =>
         {

src/HostApplication/Extensions/LanguageExtensions.cs

@@ -0,0 +1,31 @@
+namespace DentallApp.HostApplication.Extensions;
+
+public static class LanguageExtensions
+{
+    public static IServiceCollection ConfigureLanguages(
+        this IServiceCollection services,
+        IConfiguration configuration)
+    {
+        services.Configure<RequestLocalizationOptions>(options =>
+        {
+            List<CultureInfo> supportedCultures = [];
+            var languages = configuration.GetLanguages();
+            foreach (var language in languages)
+                supportedCultures.Add(new CultureInfo(language));
+
+            var defaultLanguage = configuration.GetDefaultLanguage();
+            options.DefaultRequestCulture = new RequestCulture(defaultLanguage);
+            options.SupportedCultures = supportedCultures;
+            options.SupportedUICultures = supportedCultures;
+        });
+        return services;
+    }
+
+    public static string[] GetLanguages(this IConfiguration configuration)
+        => configuration
+            .GetRequiredSection("Languages")
+            .Get<string[]>() ?? [];
+
+    public static string GetDefaultLanguage(this IConfiguration configuration)
+        => configuration.GetValue<string>("DefaultLanguage") ?? "es";
+}

src/HostApplication/Extensions/SwaggerGen.cs

@@ -5,7 +5,8 @@ public static class SwaggerGen
     public static IServiceCollection AddSwagger(this IServiceCollection services)
     {
         services.AddSwaggerGen(options =>
-        { 
+        {
+            options.OperationFilter<AcceptLanguageHeaderParameter>();
             options.EnableAnnotations();
             options.SwaggerDoc("v1", new OpenApiInfo { Title = "DentallApi", Version = "v1" });
             options.AddSecurityDefinition("Bearer", new OpenApiSecurityScheme
@@ -27,7 +28,7 @@ public static IServiceCollection AddSwagger(this IServiceCollection services)
                             Id = "Bearer"
                         }
                     },
-                    new string[] { }
+                    Array.Empty<string>()
                 }
             });
             var coreAssemblyName = typeof(GetDependentsByCurrentUserIdUseCase).Assembly.GetName().Name;
@@ -44,4 +45,31 @@ public static IServiceCollection AddSwagger(this IServiceCollection services)
         });
         return services;
     }
+
+    private class AcceptLanguageHeaderParameter(IConfiguration configuration) : IOperationFilter
+    {
+        public void Apply(OpenApiOperation operation, OperationFilterContext context)
+        {
+            operation.Parameters ??= [];
+            var languageOptions = new List<IOpenApiAny>();
+            var languages = configuration.GetLanguages();
+            var defaultLanguage = configuration.GetDefaultLanguage();
+            foreach (var language in languages) 
+                languageOptions.Add(new OpenApiString(language));
+
+            operation.Parameters.Add(new OpenApiParameter
+            {
+                Name = "Accept-Language",
+                Description = "Language preference for the response.",
+                In = ParameterLocation.Header,
+                Required = false,
+                Schema = new OpenApiSchema
+                {
+                    Type = "string",
+                    Default = new OpenApiString(defaultLanguage),
+                    Enum = languageOptions
+                }
+            });
+        }
+    }
 }

src/HostApplication/GlobalUsings.cs

@@ -16,11 +16,13 @@
 global using DentallApp.Shared.Configuration;
 
 global using System.Reflection;
+global using System.Globalization;
 global using System.Net;
 global using System.Text;
 global using System.Text.Encodings.Web;
 global using System.Text.Json.Serialization;
 
+global using Microsoft.AspNetCore.Localization;
 global using Microsoft.AspNetCore.Mvc.ApplicationParts;
 global using Microsoft.AspNetCore.Authentication;
 global using Microsoft.AspNetCore.Authentication.JwtBearer;
@@ -31,6 +33,8 @@
 global using Microsoft.Extensions.Options;
 global using Microsoft.Extensions.DependencyInjection.Extensions;
 global using Microsoft.OpenApi.Models;
+global using Microsoft.OpenApi.Any;
+global using Swashbuckle.AspNetCore.SwaggerGen;
 global using EntityFramework.Exceptions.Common;
 
 global using DotEnv.Core;

src/HostApplication/Program.cs

@@ -25,6 +25,7 @@
 builder.Services.AddSwagger();
 builder.Services.AddAuthenticationJwtBearer(appSettings);
 builder.Services.AddValidators();
+builder.Services.ConfigureLanguages(builder.Configuration);
 
 builder.Services
     .AddExceptionHandler<ReferenceConstraintExceptionHandler>()
@@ -44,8 +45,7 @@
     app.UseExceptionHandler("/");
 }
 
-app.UseRequestLocalization(appSettings.Language);
-
+app.UseRequestLocalization();
 app.UseWebSockets()
    .UsePathBase(new PathString("/api"))
    .UseRouting()

src/HostApplication/appsettings.json

@@ -1,6 +1,11 @@
 {
-    "MicrosoftAppType": "",
-    "MicrosoftAppId": "",
-    "MicrosoftAppPassword": "",
-    "MicrosoftAppTenantId": ""
+  "MicrosoftAppType": "",
+  "MicrosoftAppId": "",
+  "MicrosoftAppPassword": "",
+  "MicrosoftAppTenantId": "",
+  "DefaultLanguage": "es",
+  "Languages": [
+    "es",
+    "en"
+  ]
 }

src/Shared/Configuration/AppSettings.cs

@@ -7,7 +7,6 @@ public class AppSettings
 {
     public string BusinessName { get; set; } = string.Empty;
     public string DentalServicesImagesPath { get; set; } = string.Empty;
-    public string Language { get; set; } = string.Empty;
 
     public string AccessTokenKey { get; set; } = string.Empty;
     public double AccessTokenExpires { get; set; }